Along with the rapid development of electronic industry, it is not uncommon to play sound effect with advance sound and visual effects on computers anymore. Therefore, the requirement for video and audio performance has become more and more stringent. Except for the need of higher resolution and visual quality, in the field of audio frequency and sound effect, multi-channel sound effect has gradually replaced stereo sound effect and the mono sound effect. In an attempt to provide a more realistic or engulfing listening experience in the home theater, several techniques have developed multi-channel audio formats. Each audio channel of the multi-channel signal is routed to one of several speakers distributed throughout the home theater, providing the sound effect with the sensation that sounds are originating all around them. As the home entertainment system market expands, other multi-channel systems will likely become available to home consumers. Humans are able to localize a sound to the right or left based on arrival time and sound level differences discerned by each ear.
Head related transfer functions (HRTFS) are used to simulate positional and virtual images three-dimensional (3-D) sound using fixed speaker locations. The shape of the human head, body and auditory system affect how the brain perceives the position of sound sources. An HRTF is a characterization of the human head, body and auditory system. Thus, the HRTF is affected by the size and shape of the head, the size and shape of the pinnae, the characteristics of the ear canal. The HRTF is typically a function of both frequency and relative orientation between the head and the source of the sound field. The HRTF accounts for the frequency response, frequency filtering, delays and reflections inherent in the human head. By adjusting the frequency and delays of audio signals according to the HRTF, three-dimensional sound can be simulated from fixed speaker locations. U.S. Pat. No. 5,729,612 entitled “Method and apparatus for measuring head-related transfer functions”, which disclosed a method for accurately deriving acoustic transfer functions such as head-related transfer functions at low cost. The prior art is filed on Aug. 5, 1994.
A unique HRTF can be calculated for each individual by performing detailed and time-consuming measurements of the head, ear and body. The measurements taken for an individual are converted to a transfer function usable by a processing device to adjust the characteristics of audio signal outputs to individual earphones to simulate positional three-dimensional sound.
Because HRTF simulates the sound effect model heard by a human ear in a three-dimensional space and the parameters corresponding to the three-dimensional sound effect at every spot of the space are determined by its distance, azimuth, and elevation, the listener feel like within the real atmosphere of the sound while playing the sound effect. The Head Related Transfer Function uses an artificial head or put microphones within human ears. Each sound source has to be measured from 20 HZ.about.20 KHZ and the result is preliminary HRTF library. The preliminary HRTF library, via mathematical process, generates parameters needed by DSP digital filter. As long as mono wave sound is processed by the left and the right digital filters, it can emulate 3D positional audio by means of earphones.
HRTF 3D Positional Audio in PC Applications includes simulating multi-speaker Surround with two physical speakers to deliver five “virtual speakers” into space surrounding the listener and enabling home theater sound effects. However, the 5.1 CH DVD or 4 CH 3D game uses HRTF to create virtual speakers on rear side to replace physical speaker for DVD and 3D game meets some problems. The ear-phone device do not have the ability to offer good bass. The bass wavelength is longer than the size of human head, thus there is no direct information on bass due to the structure of the earphone device. Bass speaker called sub-woofer speaker is good for all channels. It is unfortunately, the rear side bass has to be filtered out from rear signal.
There is a great need for sound control system to overcome the difficulties mentioned above.